A flow channel, in particular a hot runner, is used in injection-moulding technology for feeding a flowable compound—for example a polymer melt—at a predeterminable temperature and under high pressure into a mould impression of a moulding tool (for example a mould plate). A special portion of a flow channel may be formed by an injection-moulding nozzle. These usually comprise a material tube with a flow channel which ends in a nozzle mouthpiece. The latter forms at the end a nozzle outlet opening, which opens out into the mould impression by way of a gate.
In order that the flowable compound does not cool down prematurely within the hot runner or flow channel, electrical heating elements with heating conductors are used. Their electrical conductors can be led out from the injection-moulding tool, which comprises the flow channel and the moulding tool, by way of cables. In this case, the connections to the heating elements are exposed to high temperatures and strong shocks and vibrations. This applies in particular to heating elements that are arranged on the outside of the material tube of an injection-moulding nozzle. Usually, not much free installation space is available in this area. In a particular configuration, the heating elements have a sleeve-shaped carrier element and an electrical conductor, which generates heat when an electrical voltage is applied or an electrical current flows through.
The same problems arise during the heating of a mould impression. Here, too, the heating element that is possibly applied to a portion of the wall or incorporated in the wall of the mould impression is exposed to strong shocks and vibrations, whereby the connections of the heating element are subjected to corresponding loads. In addition to this, space is usually confined, making it more difficult to provide a permanently reliable electrical connection.
The electrical conductor may—as disclosed for example in DE 10 2006 049 669 A1—be a heating coil formed from resistance wire. U.S. Pat. No. 4,486,650 A discloses in combination with a heating coil for example a releasable plug-in connection between the connection ends of the heating coil and the connection line of a power supply.
In the following, a thick-film heating on a cylindrical carrier element is taken as a basis by way of example. The invention is not restricted to this, however, but can also be applied in the same way to other types and forms of heating elements.
DE 10 2006 049 667 A1 uses so-called thick-film heating elements applied as heating conductor paths to a sleeve as a carrier element by the screen printing process. Optionally provided between the carrier element and the electrical conductor is an insulating layer, which is likewise applied by the screen printing process as a thick film. To keep the overall size of the heating element particularly small, the carrier element may—as described in DE 199 41 038 A1—also be directly the material tube of an injection-moulding nozzle.
In order to supply the thick-film heating with energy, a connection contact is respectively provided at the ends of the heating conductor path, for example in the form of a pigtail or a connection pin (see in this respect WO 2005/053361 A2, DE 10 2008 004 526 A1 or DE 10 2008 015 376 A1). By way of the connection contact, the heating conductor path is connected to the connection line of a power source.
DE 10 2012 101 400 A1 also discloses an injection-moulding nozzle with an electrical heating element which comprises a connection device for producing an electrical connection to a connection line, wherein connection contacts of the heating element end in an insulator of the connection device that electrically separates the connection contacts from one another. The connection line has contact elements, which can be brought into electrical contact with the connection contacts of the heating element, wherein the insulator is arranged at least in certain portions in a receiving sleeve of the connection device. The connection line has here at the end a plug or a coupling, which can be releasably fixed in or on the receiving sleeve in such a way that the contact elements of the connection line electrically contact the connection contacts of the heating element. A first end of the receiving sleeve, pointing in the direction of the heating element, reaches around the insulator. At this first end, the receiving sleeve also has two feet pointing outwards opposite from one another and fastened to the heating element.
A disadvantage of this configuration is that the connection as a whole has a great overall height, reaching up from the heating element. Installation space for this is required in the injection-moulding tool. The arrangement of flow channels and further injection-moulding nozzles in this installation space is consequently ruled out. Similarly, the forming of the mould impression is restricted. It is also problematic that the relatively high construction forms a relatively long lever arm, which transfers tension on the cable to the connection device and can destroy it.